Contact printer and method of making a filter for a contact printer

ABSTRACT

A method of improving uneven illumination in a contact printer having an original image position and a light source to illuminate the original image position, which light source may illuminate the original image position non-uniformly, the method comprising: first forming a mask by exposing a photographic element to the light source and processing the element to form a negative image of the light source at a filtering position between the light source and the original image position; and positioning the mask at the filtering position. A second aspect of the method uses an electronic processor and gathered illumination data, to generate a mask.

FIELD OF THE INVENTION

The invention relates generally to the field of printing images,particularly integral images, using photographic printing, andparticularly using contact printing.

BACKGROUND OF THE INVENTION

It is well known to copy an original image using a photographic printingtechnique in which a photosensitive element is exposed to light from theoriginal image. In contact printing an original image is printed bypositioning a light sensitive element in contact with an originaltransparency carrying the image, so that light from a light sourcepasses through the original image onto the light sensitive element.Since no lens systems are required and the original image is adjacentthe light sensitive element, the print exhibits very low degradationfrom the original image.

Contact printing then, is particularly desirable in cases where it isnecessary to maintain a very high resolution in the print. There aremany uses of contact printing in the areas of high quality film andlithographic reproduction for images, circuit boards and integratedcicuits. Another example is in the printing of integral images. Failureto maintain a high resolution may cause individual image segments orline segments, to overlap in the print leading to an undesirable image.

Integral image elements themselves are well known. For example, knownintegral image elements include those which use a lenticular lens sheet,fly's eye lens sheet, or barrier strip sheet and a three-dimensionalintegral image aligned with the sheet, so that a user can view thethree-dimensional image without any special glasses or other equipment.Such imaging elements and their construction, are described in"Three-Dimensional Imaging Techniques" by Takanori Okoshi, AcademicPress, Inc., New York, 1976. Integral image elements having a lenticularlens sheet (that is, a sheet with a plurality of adjacent, parallel,elongated, and partially cylindrical lenses) are also described in thefollowing Unites States patents: U.S. Pat. No. 5,391,254; U.S. Pat. No.5,424,533; U.S Pat. No. 5,241,608; U.S. Pat. No. 5,455,689; U.S. Pat.No. 5,276,478; U.S. Pat. No. 5,391,254; U.S. Pat. No. 5,424,533 andothers; as well as allowed U.S. patent application Ser. No. 07/931,744.Integral image elements with lenticular lens sheets use what isreferenced as a lenticular image having interlaced vertical image sliceswhich. In the case of a three-dimensional lenticular image, these imageslices are aligned with the lenticules so that a three-dimensional imageis viewable when the lenticules are vertically oriented with respect toa viewer's eyes. The image may be conveniently laminated (that is,adhered) to an integral or lenticular lens sheet. Similar integral imageelements, such as described in U.S. Pat. No. 3,268,238 and U.S. Pat. No.3,538,632, can be used to convey a number of individual two-dimensionalscenes (such as unrelated scenes or a sequence of scenes depictingmotion) rather than one or more three-dimensional images. Integral imageelements using reflective layers behind the integral image to enhanceviewing of the integral image by reflected light, are also described inU.S. Pat. No. 3,751,258, U.S. Pat. No. 2,500,511, U.S. Pat. No.2,039,648, U.S. Pat. No. 1,918,705 and GB 492,186.

While contact printing an original image, such as an original image,does not produce a print with as much degradation than might occur usingan enlarger for printing, for example, it is not perfect. It is knownthat the light source used to illuminate the original image will notilluminate the original image completely uniformly. Typically, with aprojection type light source, this means that the center of the printwill tend to be darker (where the print is a negative). In an attempt tocorrect for this, a sequence of discrete filters has been used betweenthe light source and original image, such that overall the sequenceexhibits incremental decreases in density moving from the center to theperiphery. However, this technique requires manually estimating thelight intensity variance at the original image position, estimating asuitable filter sequence and then constructing it. Inherent errors inthese steps will inevitably lead to poor correction for light intensityvariance. Additionally, at the edges of the overlapping filters therewill be a sudden drop in overall density and hence a sudden drop inlight intensity.

It would be desirable then, to provide a means for improvingillumination uniformity at the original image position in a contactprinter, which is simple to implement and which does not produce at theoriginal image position, edges across which there is a sudden variationin light intensity.

SUMMARY OF THE INVENTION

The present invention therefore provides a method of improving unevenillumination in a contact printer having an original image position anda light source to illuminate the original image position, which methodcomprises in one aspect:

first forming a mask by exposing a photographic element to the lightsource and processing the element to form a negative image of the lightsource at a filtering position between the light source and the originalimage position; and

positioning the mask at the filtering position.

In a second aspect the method of the present invention comprises:

inputting into a computer, data representative of illumination atmultiple laterally spaced locations positioned in a direction from thelight source to the original image position;

processing the data in the computer to form a mask image which whenprinted on a support and placed at a filtering position between thelight source and the original image position, improves illuminationuniformity at the original image position;

printing the mask image on the support; and

positioning the mask at the filtering position.

The present invention further provides a contact printer using a maskformed by either aspect of the method of the present invention.Additionally, the present invention provides a computer readable storagemedium carrying program means. The program means includes any suitablecomputer readable program code which can be used by a computer toexecute each of the calculation steps of the present invention.

The present invention then, provides in any aspect, a simple techniqueof improving upon illumination uniformity in a contact printer. In thecase of the first aspect, upon exposure and processing, the maskautomatically has higher densities at the locations where the mostfiltering is needed, and has no edges across which abrupt changes inoptical density occur (unless they correspond to edges on the originalimage position across which corresponding abrupt changes in lightintensity occur). In the case of the second aspect, use of the computerallows ready manipulation of the illumination data to generate the mask,even though the illumination data may only be from a few points and mayrepresent illumination at a different location than the filteringposition (in which case computer manipulation of the data avoidsphotographic enlargement or reduction of the mask image). Improvedillumination uniformity at the original image position provides higherquality images, including integral images, and is particularlybeneficial where the original image includes a plurality of independentimages (the copies of which are separated).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a contact printer of the presentinvention;

FIG. 2 is a cross-section along the line 2--2 in FIG. 1;

FIG. 3 is a block diagram of an electronic system for generating a mask;and

FIG. 4 is a flowchart illustrating a method of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

EMBODIMENTS OF THE INVENTION

Referring first to FIGS. 1 and 2, the contact printer 2 has a printerhousing 3 and a transparent glass platen 4 at an upper end of printerhousing 3, an upper surface 5 of which platen 4 serves as an originalimage position. Beneath and just outside the lateral extent of platen 4,are positioned four elongated brackets 14 (only two of which are seen inFIG. 2) each having a set of slots 16 so as to hold a rectangular maskin any of six possible positions adjacent platen 4 (only the uppermostposition being immediately adjacent platen 4). A light source 6 ispositioned at a lower position inside printer housing 3. Light source 6includes an electric lamp and reflector assembly 8, positioned inside alamphouse 10. Lamphouse 10 is essentially completely closed except foran upper opening 11. One or more color and/or contrast filters, or otherfilters, may be present immediately above lamp and reflector assembly 8at position 9. Light source 6 acts as a projection light source in thatlight from light source 6 diverges at an angle in the direction ofplaten 4, in a manner most clearly shown by the broken lines in FIG. 2.

Contact printer 2 also includes a mask designated 18b in FIG. 1, whichis positioned in the direction of platen 4 from light source 6(specifically, between light source 6 and platen 4). In FIG. 2 is shownan alternate mask 18a, as well as a second alternate mask 18c. Mask 18cis at a filtering position adjacent light source 6. Masks 18b and 18care held in their respective filtering positions by a suitable structure(not shown). Mask 18a is in a location which is preferred from theperspective of providing best uniformity of illumination at the originalimage position. However, film grain of mask 18a may be printed duringoperation of contact printer 2. On the other hand, mask 18c is at aposition which will minimize the chance of film grain appearing in aprint produced by contact printer 2. However mask 18c provides lessprecision in controlling illumination uniformity.

Each mask 18a, 18b or 18c is a generally transparent sheet but carries amask image which, in the case of a mask prepared by the first aspect ofthe method of the present invention, is a negative image of light source6 at the corresponding position for that mask (which position isreferenced as a filtering position). Thus, in the contact printer shownwith a projection light source 6, the mask image will tend to have ahigher density (that is, lower light transmission) toward its centersince illumination from light source 6 will tend to be higher at thecenter than the periphery of each mask 18a, 18b and 18c. As will bedescribed further shortly, in this way any of the masks can reduce anynon-uniformity of illumination reaching upper surface 5 of platen 4 fromthat which would otherwise occur absent the mask. Uniformity ofillumination across upper surface, can, for example, be measured as thestandard deviation or variance in illumination reaching a statisticallysignificant number of points across upper surface 5. Masks 18a, 18b, and18c are essentially similar to one another, and being at differentlocations in the projected light from light source 6 are appropriatelysized.

Any of masks 18a, 18b or 18c can be made using the method of the firstor second aspects of the present invention.

If the mask is to be made using the first aspect of the method of thepresent invention (photographic method), a light sensitive photographicelement is positioned at an exposure position and exposed to light fromlight source 6 at that position. The exposure position may broadly beany position from the light source in the direction of upper surface 5(which again, serves as the original image position), including adjacent(but above) light source 6 or even above upper surface 5. However, theexposure position is preferably between light source 6 to the uppersurface 5, and most preferably is the same as the filtering position(that is, the position at which the resulting mask will be used). Thephotographic element is then processed to form a negative image of thelight source at the exposure position. If the exposure position isfurther from (or closer to) lamp source 6, than is the filteringposition for the mask being made, then as part of the processing themask image should be reduced (or enlarged) in size so that it willextend across the projection of light from light source 6 at the chosenfiltering position (as illustrated in FIG. 2). This reduction orenlargement can be conveniently accomplished by a photographic processusing an enlarger.

The photographic element used to form the mask can be any lightsensitive element (such as a light sensitive element using a silverhalide emulsion). By a "negative" image of the light source is meantthat areas of higher light intensity will appear darker. Thephotographic element used will typically be one designed to produce anegative image (designated as a "negative" film, or some other meansassociated with the film to indicate that it is intended for producing anegative image), and will be processed by a negative process (which fora silver halide element will mean processing with a developer and fixingthe resulting negative image). A black and white film will preferably beused in which the image is formed by developed silver, although a filmforming a dye image could be used but is less preferable (since somecoloring on the processed element may become apparent). It will beappreciated that the exposure duration and processing should be selectedfor the particular photographic element used to generate the necessarynegative image of the light source so as to reduce non-uniformity ofillumination from light source 6 which would otherwise reach uppersurface 5 (the original image position). Ideally, the gamma of theprocessed element will be 1 or close to 1 and the lowest density of themask will be the minimum density of the mask material. Gamma is a wellunderstood term and is described, for example, in T. H. James, editor,The Theory of the Photographic Process, 4th Edition, Macmillan, NewYork, 1977 (particularly p. 502).

Referring to FIG. 3, this illustrates an apparatus for forming the maskaccording to a method of the second aspect of the present invention. Inparticular, FIG. 3 shows a scanner 30 for scanning an exposed andprocessed photographic element and converting optical densitymeasurements into digital data. Scanner 30 may be any conventional blackand white scanner. A color scanner could also be used but is notrequired. Scanner 30 is connected to a processor 32 which receivesinstructions for all steps to be executed in processor 32, from anysuitable program code held in memory 33. Processor 32 is in turnconnected to a monitor 34 and a user input device 36, such as a keyboardand/or pointing device (such as a mouse).

Processor 32, memory 33, monitor 34 and input device 36 may becomponents of a general purpose digital desktop computer programmed toexecute the method described below. The programming may be provided tothe memory 33 of the computer on any computer readable storage mediumcarrying the program. The computer readable storage medium may comprise,for example: magnetic storage media such as magnetic disc (such as afloppy disc or a hard disc drive) or magnetic tape; optical storagemedia such as optical disc, optical tape, or machine readable bar code;solid state electronic storage devices such as random access memory(RAM), or read only memory (ROM); or any other physical device or mediumwhich might be employed to store a computer program.

A printer 38, preferably a film recorder, is connected to receive maskimage data from processor 32 and print the image on a transparency.Printer 38 can be any suitable printer, such as a black and white onlyprinter, although color printers could be used (preferably which have ablack dye for example black and white photographic film). Preferably ahigh resolution film recorder is used as printer 38 to avoid visibleedges at which a noticeable drop in density might occur. One suchsuitable printer is an LVT printer available from Eastman Kodak Company,Rochester, N.Y.

In the method to be executed by the apparatus of FIG. 3, a photographicelement is first exposed to light source 6 at some position in adirection of upper surface 5 (the original image position). Typically,the element will be exposed on upper surface 5. The exposed andprocessed element then, will carry data representative of illuminationat multiple laterally spaced locations. These locations are all on thesame plane of the element. However, it is not essential for suchlocations to be coplanar provided that data on their relative distancelight source 6 is provided to processor 32, such as through input device36 and processor 32 is programmed to compensate for the difference inrelative distances. For simplicity, the element and processing areselected such that a negative image is formed. However, this is notnecessary. It will be appreciated that provided a user indicates throughinput device 36 whether a negative or positive image is being provided,processor 32 can perform the necessary processing to form the maskimage. Nor is it necessary that the processed element exhibit a gamma of1 since a user can input the gamma value in input device 36 andprocessor 32 can be programmed to correct density data from scanner 30based on the input gamma value. One of the advantages in using themethod of the second aspect of the present invention, is that regardlessof how the illumination data is obtained and input to, processor 32 canbe suitably programmed to compensate as necessary to still produce amask image which, when printed to form a mask and positioned at afiltering position, will reduce illumination non-uniformity at uppersurface 5.

Processor 32 can receive the digital data from scanner 30 directly, asshown in FIG. 3, or alternatively the digital data could be first orlater stored in a suitable memory (not shown) such as RAM, magnetic oroptical memory devices. Processor 32 is suitably programmed to convertthe illumination data into the required mask image based on factorsalready discussed, such as the locations from which the illuminationdata was obtained, as well as the desired position at which the maskwill be used. In this regard it will be seen that another advantage ofthe method of the second aspect of the present invention is thatprocessor 32 can enlarge or reduce mask image size as required, usingwell known digital image processing algorithms, depending upon therelative locations at which the illumination data was obtained and theposition at which the mask will be used. These relative locations can bespecified through input device 36.

The mask image data generated by processor 32 can then be sent toprinter 38 (again, preferably a film recorder) for printing on asuitable transparency (in the case of the preferred film recorder, ablack and white silver halide film). The resulting mask is thenpositioned in contact printer 2 at the previously selected position.

The mask image data on line 39 (going to printer 38) to produce theresulting density or transmittance values of the resulting mask isgenerated by performing the steps steps outlined below. However, not allthe steps need necessarily be performed in the order specified.

A test image is made using printer 38 following the same printingprocess as will be used to make the final mask. This test imagecomprises a series of test patches generated by specific data values, p,which cover a range of possible values that can be transferred toprinter 38 on line 39. It is not necessary to have every possible valuerepresented by a patch.

The test image that is printed using the same printing procedure thatwill be used for the final mask, is measured. This process involvesmeasuring the transmission, T, of each printed patch on the printed testimage. The transmission value, T (defined as the ratio of lightintensity coming from the mask at a given location x,y to the lightintensity incident on the mask at the same location) is measured foreach printed patch. These patch values are correlated with the value pon line 39 used to create the specific patch of measured T.

Using regression or trendline techniques a transfer function, T_(p) (p),is created. T_(p) (p) may be in the form of an equation or a look-uptable. The transfer function derived from the relationship between thetransmittance T at a patch in response to the specific data input valuesp on line 39 to print that location is defined as T_(p) (p).

Input data corresponding to the non-uniformity of the intensity ofillumination, I, across the platen is measured at discrete pointslocated at positions x,y on upper surface 5 of platen 4. This input datafor such positions is defined as I(x,y). Measurement of I(x,y) can beaccomplished using any suitable device, such as photo-detectors,scanners, CCD cameras, or by exposing film which is then scanned. Forsome of these inputs it will be necessary to make a conversion from themeasured value to intensity. The minimum of I(x,y) is defined as I_(min)and the maximum is I_(max).

The maximum achievable transmission ratio of the mask 18 is alsodetermined by using a test sample which is close to the minimum densityof the mask, D_(min), (such as a patch on the test image which has noprinting upon it). The transmission value T for such a test sample isdefined as T_(max), and corresponds to the intensity of light passingthrough the mask at a location where there is no printing, divided bythe intensity of the light incident on the mask at a specific point.

The value of the required printer data values as a function of position,p(x,y), is computed by processor 32. Assuming the mask is to be againstupper surface 5 of platen 4 the intensity of the signal generated byprocessor 32 and passed on line 39 to printer 38 is: ##EQU1## where K isa constant of value 0.9 to 0.95 to provide a margin so that the printer38 does not saturate, and T_(p) ⁻¹ is the inverse of T_(p) (p). All ofthe required calculations can be readily executed in processor 32 whichhas access to the necessary program instructions in memory 33.

Illumination values for every point (x,y) will not likely actually bemeasured. In order to obtain a mask without edges across which there aresignificant changes in transmission, for those positions at whichillumination data was not measured, processor 32 can have suitableprogram code which can interpolate between, or extrapolate from,meausured illumination values or calculated printer code values. Thisinterpolation/extrapolation could generate either I(x,y) values or beused to directly calculate p(x,y) values for those locations at whichillumination values were not actually measured. Any such suitableprogram code then, acts as means for interpolating or extrapolating toobtain mask image values at locations other than those for which datarepresentative of illumination was obtained.

The mask image data p(x,y) is next sent on line 39 to the printer 38 toprint the correction mask.

If the mask is moved back from the platen 4 by a distance d₁ as shown inFIG. 2, and if d₂ is the distance of upper surface 5 from the diffusedaperture 15 (which is preferably small in diameter), to a first order ofapproximation equation (1) becomes ##EQU2## provided the aperture 15 issmall, and x=0, y=0 falls at the center point of the mask (whichcorresponds to a center vertical axis 40 of the printer 2). Note thatthe mask image then, prior to printing, is formed as the series ofprinter data values, p(x,y). Those data values are a function of thedata representative of illumination, in this case the illuminationvalues I(x,y), and the transfer characteristic, as shown by equation (1)or (2).

The foregoing overall procedure for obtaining the printed mask image isillustrated in the flowchart of FIG. 4. Test patch data including actualprinter code values, p, and the corresponding measured transmittancevalues, T, of the printed test patches are inputted 50. These are usedby processor 32 to calculate 52 the transfer function, T_(p) (p), asdescribed above. Measured Tmax and I(x,y) values are inputted 58, 56 toprocessor 32 and the required printer data values of the mask image arecalculated 54 in accordance with equation (1) or (2) above. The maskimage may then be printed 60. If interpolation/extrapolation of printerdata values p(x,y) is required for locations at which illumination datawas not obtained, these calculations can be done by processor 32 as partof step 54.

Finally, the correction mask is positioned at the filtering position. Asa result an original image 20, such as an original integral image, canthen be printed by contact printer 2. This is done by positioningoriginal image 20 on the upper surface 5, and positioning a lightsensitive element 22 (such as unexposed film) immediately adjacent toand directly above original image 20. Light source 6 is then illuminatedto expose element 22 to light which passes through the mask 18a, 18b or18c and original image 20.

It will be appreciated (and as already mentioned) that in the method ofdetermining the non-uniformity of intensity in the step above, the inputillumination data can be obtained from any of a number of possiblesources other than a scanner 30. For example, such data could beobtained by actual direct measurement with a sensor such as a photocellwhich is manually positioned at various defined locations across theilluminated surface 4 and intensity data being recorded of each positionas input data which is keyed into processor 32 instead of using ascanner. Alternatively multiple photocells may be used. Another approachis to use a CCD array with an imaging optic or line sensor with suitableoptics, or could be obtained by visually estimating illuminationvariances at the original image position. The data "representative" ofillumination, then, may only provide relative illumination values. Incases where the illumination data obtained only represents data for alimited number of lateral locations within the light beam projected bylight source 6 (such as might be obtained from photocells readingillumination at points on upper surface 5), processor 32 can be suitablyprogrammed to estimate illumination data at other locations such as byextrapolation or interpolation, or from equations which describe theexpected distribution of light.

It will be appreciated that, the present invention can be used for allvariety of images including color and black and white as well as 2D, 3Dand integral images. The particular application of printing integralimages where even illumination and sharpness in the printed image areparticularly important to produce a visually acceptable image willbenefit considerably from this approach. Once the exposed element 22 hasbeen processed to form a fixed print of the original image 20, it canthen be aligned with a suitable integral lens sheet. While the integrallens sheet could be a fly's eye lens sheet it is more preferably alenticular lens sheet with lenticules on the front surface (in whichcase the integral image would be a lenticular image). Alternatively, theintegral lens sheet could have regions of varying indices of refractionthrough its volume configured in such a way as to provide (inconjunction with the surfaces of the sheet, such as a curved externalsurface, flat external surface or some other shape) the same opticaldeflection of light rays as would be provided by a conventional fly'seye or lenticular lens sheet. Also, the back surface of the lens sheetmay also be curved so as to either strengthen the lens effect orcompensate for the curved focal plain which may be inherent in the lensconstruction. Consequently, the curvature on the back side may be the ofsuch a shape as to match the curvature of the focal plain of the lens.

Further, as described above, by an "integral" image is referenced animage composed of segments (lines, in the case of a lenticular lenssheet) from at least one complete image (and often more than one image),which segments are to be aligned with respective individual lenses of anintegral lens sheet so that each of the one or more images is viewablewhen a user's eyes are at the correct angle relative to the imagingelement. The integral image can be one or more three-dimensional images,one or more two dimensional images, or any combination of the foregoing.By a "three-dimensional image", is meant an integral image which, whenviewed through the lens, has a visible depth element. A depth elementmeans the ability to at least partially look around an object in thescene. This can be obtained by interlacing lines from differentperspective views of the same scene (that is, views from differentangular positions with respect to the scene). Thus, a three-dimensionalimage necessarily includes at least two views of a scene. By atwo-dimensional image is referenced an image which, when viewed in thefinal product, does not have any viewable depth element.

The invention has been described with reference to a preferredembodiment. However, it will be appreciated that variations andmodifications can be effected by a person of ordinary skill in the artwithout departing from the scope of the invention.

    ______________________________________                                        PARTS LIST                                                                    ______________________________________                                         2                  Contact Printer                                            3                  Printer Housing                                            4                  Platen                                                     5                  Upper Surface                                              6                  Source                                                     8                  Assembly                                                   9                  Position                                                  10                  Lamphouse                                                 11                  Upper Opening                                             14                  Brackets                                                  15                  Aperture                                                  16                  Slots                                                     18a, 18b, 18c       Masks                                                     20                  Original Image                                            22                  Element                                                   30                  Scanner                                                   32                  Processor                                                 34                  Monitor                                                   34                  Processor                                                 36                  Input Device                                              38                  Printer                                                   39                  Line                                                      40                  Axis                                                      50-60               Steps                                                     ______________________________________                                    

We claim:
 1. A method of improving uneven illumination in a contactprinter having an original image position and a light source toilluminate the original image position, which light source mayilluminate the original image position non-uniformly, the methodcomprising:first forming a mask by exposing a photographic element tothe light source and processing the element to form a negative image ofthe light source at a filtering position between the light source andthe original image position; and positioning the mask at the filteringposition.
 2. A method according to claim 1 wherein the photographicelement is a silver halide element which is processed by a negativeprocess.
 3. A method of improving uneven illumination in a contactprinter having an original image position and a light source toilluminate the original image position, which light source mayilluminate the original image position non-uniformly, the methodcomprising:first forming a mask which will be positioned at a filteringposition between the light source and the original image position, byexposing to the light source a photographic element at an exposureposition from the light source in the direction of the original imageposition, and processing the element to form a negative image, where theexposure and filtering positions may be the same or different; andpositioning the mask at the filtering position; wherein when theexposure and filtering positions are different, the processing includesreducing or enlarging the negative image.
 4. A method according to claim3 additionally comprising exposing a light sensitive element positionedadjacent the original image position to light passing through the maskand the original image from the light source, to form a print of theoriginal image on the light sensitive element.
 5. A method according toclaim 4 wherein the original image is an integral image.
 6. A methodaccording to claim 4 wherein the original image includes a plurality ofindependent images, the method additionally comprising, after exposureof the light sensitive element, separating the copies of the pluralityof independent images formed on the light sensitive element.
 7. A methodaccording to claim 3 wherein the exposure and filtering positions arethe same.
 8. A method according to claim 3 wherein the exposure andfiltering positions are different.
 9. A method according to claim 3wherein the exposure and filtering positions are at or adjacent theoriginal image position.
 10. A method according to claim 1 wherein thedensity distribution of the mask is such that the light reaching theoriginal image position from the light source and through the maskpositioned at the second position, is substantially uniform inintensity.
 11. A method according to claim 5 wherein the light source isa projection light source.
 12. A contact printer comprising:an originalimage holder to hold an original image to be printed at an originalimage position; a light source to illuminate the original imageposition; and a mask positioned at a filtering position between thelight source and the original image position, which mask is aphotographic element which was exposed to the light source and processedto form a negative image of the light source at the filtering position.13. A contact printer according to claim 12 wherein the mask was exposedat an exposure position which is substantially the same as the filteringposition.
 14. A contact printer according to claim 12 wherein the maskis positioned at a filtering position which is adjacent the originalimage position.
 15. A contact printer according to claim 12 wherein themask was exposed at an exposure position, wherein the exposure andfiltering position are both at or adjacent the original image position.16. A contact printer according to claim 12 wherein the mask ispositioned adjacent the light source.
 17. A contact printer according toclaim 12 wherein the mask is positioned between the light source and theoriginal image position.
 18. A contact printer according to claim 12wherein the light source is a projection light source.
 19. A method ofimproving uneven illumination in a contact printer having an originalimage position and a light source to illuminate the original imageposition, which light source may illuminate the original image positionnon-uniformly, the method comprising:inputting into a computer, datarepresentative of illumination at multiple laterally spaced locationspositioned in a direction from the light source to the original imageposition; processing the data in the computer to form a mask image whichwhen printed on a support and positioned at a filtering position betweenthe light source and the original image position, improves illuminationuniformity at the original image position; printing the mask image on asupport; and positioning the mask at the filtering position.
 20. Amethod according to claim 19 additionally comprising printing a seriesof test patches of different optical density corresponding to datavalues sent to the printer, measuring the optical density of the printedtest patches and determining as a density transfer characteristic therelationship between data values sent to the printer and thecorresponding printed optical density.
 21. A method according to claim20 wherein the mask image, prior to printing, is formed as a series ofprinter data values which are a function of the data representative ofillumination and the transfer characteristic.
 22. The method of claim 19wherein the data representative of illumination is obtained from asensor which measures illumination at multiple locations on the originalimage position.
 23. The method of claim 19 wherein the step of inputtinginto the computer, data representative of illumination, comprisesexposing to the light source a photographic element at an exposureposition from the light source in the direction of the original imageposition, and processing the element to form an image of the lightsource, where the exposure and filtering positions may be the same ordifferent; andscanning the exposed and processed original image toobtain the data representative of illumination.
 24. A method accordingto claim 23 wherein at least some of the data represent illumination ata distance from the light source which is different from the distance ofthe filtering position from the light source, and wherein the step ofprocessing the data to form the mask adjusts the density of the mask asa function of the differences in the distances.
 25. A method accordingto claim 19 additionally comprising exposing a light sensitive elementpositioned adjacent the original image position to light passing throughthe mask and the original image from the light source, to form a printof the original image on the light sensitive element.
 26. A methodaccording to claim 25 wherein the original image is an integral image.27. A method according to claim 26 wherein the integral image is alenticular image.
 28. A method according to claim 27 additionallycomprising aligning the lenticular image print with a lenticular lenssheet.
 29. A contact printer comprising:an original image holder to holdan original image to be printed at an original image position; a lightsource to illuminate the original image position; and a mask positionedat a filtering position between the light source and the original imageposition, which mask carries a computer printed image obtained fromcomputer processing of data representative of illumination at multiplelaterally spaced apart locations positioned in a direction from thelight source to the original image position, such that the mask improvesillumination uniformity at the original image position.
 30. A computerprogram product, comprising: a computer readable storage mediumincluding program means which comprises:means for receiving datarepresentative of illumination at multiple laterally spaced locationspositioned in a direction, in a contact printer, from a light source ofthe printer to an original image position of the printer; means forprocessing the data in the computer to form a mask image which whenprinted on a support and positioned at a filtering position between thelight source and the original image position, improves illuminationuniformity at the original image position; means for processing the datain a computer to form a mask image which when printed on a support andpositioned at a filtering position between the light source and theoriginal image position, improves illumination uniformity at theoriginal image position; means for causing a printer connected to thecomputer to print the mask image on the support.
 31. A computer programproduct according to claim 30 wherein the means for processing includesmeans for interpolating or extrapolating to obtain mask image values atlocations other than those for which data representative of illuminationwas obtained.